Field of the Invention
The present invention relates to a fluorescent substance, and a production method of the fluorescent substance.
Description of the Related Art
Recently, a mainstream of fluorescent excitation light using blue LED has been white light realized by combining blue LED and a yellow fluorescent substance. However, it lacks a red color component, and has poor color rendition. In order to improve color rendition, a combination of a green fluorescent substance and a red fluorescent substance is typically used. As for the red fluorescent substance, a fluorescent substance that can control a wavelength in the red color region, and has a narrow half width. However, a fluorescent substance that can be used on practice has not been known among red fluorescent substances.
A CaS:Eu-based fluorescent substance has a relative narrow half width of emission, exhibits deep red, and can realize a wide color range. Therefore, the CaS:Eu-based fluorescent substance has been noted as a red-light emitting fluorescent substance for blue LED excitation.
For example, disclosed as a red and green fluorescent substance suitable for electron beam excitation is a fluorescent substance represented by the general formula CaS1-XSeX:A (where A is at least one element selected from the group consisting of Eu and Ce, and x is a value in the range of 0.001≦x≦0.6) (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 58-125781).
The disclosed CaS—CaSe mixed crystal-based fluorescent substance (also represented by Ca(Se, S):Eu) forms an all proportional solid solution, and an emission wavelength thereof is monotonously shifted to the shorter wavelength side, as the concentration of Se increases. In the case where an activating agent is Eu, the emission wavelength can be successively controlled in the 590 nm-655 nm band (FIG. 1).
However, it is necessary to further control an emission spectral line shape of the aforementioned fluorescent substance in order to realize practical use thereof. A fluorescent substance having a target emission wavelength, having a narrow full width at half maximum of emission, and having a sharp emission spectral line shape is desired, but the aforementioned disclosed technology has not provided a fluorescent substance having a sufficiently desirable emission spectral line shape.
Moreover, also desired is a fluorescent substance having a desired emission spectral line shape, and excellent characteristics, such as emission peak intensity, internal quantum efficiency, and external quantum efficiency. However, a fluorescent substance that gives excellent results in all of the aforementioned characteristics has not yet been attained.
Moreover, it is necessary to strictly manage a concentration of Se, which is a base of the Ca(Se, S):Eu fluorescent substance, in order to control the emission peak wavelength thereof. In the aforementioned disclose method, the management of the Se concentration is performed by mixing raw materials, CaS and CaSe at the predetermined ratio, and carrying out a heat treatment in a quartz ampoule, or carrying a heat treatment of calcium oxide precursor in a quartz reaction tube with flowing a gas to which H2S and H2Se are mixed at the predetermined ratio. However, these methods can treat only a small quantity, and are not suited for industrial use, as H2Se gas, which is toxic specialty material gas, is used.
In order to industrialize a Ca(Se, S):Eu fluorescent substance, desired is a production method, which can produce a large quantity without using any special process, and is inexpensive.